Turnbuckles such as cable stretches, rig stretchers etc are known in many different designs. The most common occuring turnbuckle consists of a left-threaded and a right-hreaded screw, threaded into a rotatable sleeve. By rotating the sleeve, the turnbuckle is extended or shortended. This and similar types of stretchers or tighteners show a number of disadvantages. Thus the threads of the turnbuckle is mostly uncovered and exposed for weather and wind, at which corrosion attack and locking-up caused thereof may result. The uncovered threads also results in that wires, canvas etc. can be torn by contacting the turnbuckle. It is very easy to turn such a turnbuckle incorrectly, i.e. upside down, so that by rotating the sleeve to the right, the screws can come loose from the sleeve and serious damages may result, if the turnbuckle for example guys a mast to a boat.
In order that the turnbuckle should not be opened unintentially, it is necessary to lock it, which generally must be done with split pins or the like, which also provides projecting sharp details, which not only can cause damages but may also be easily lost.
In order to protect ropes and sails from wear when contacting the turnbuckle it is also previously known to use a plastic turnbuckle protector, which is locked up around the turnbuckle. The protector provides a complication and is not particularly effective either, so they are easily loosened when a line is pulled around such a protector.
Especially if the turnbuckle is used on ships and boats there is a great risk that the different parts by corrosive action cling to each other, not only the threads but also the swivel. As the turnbuckle must be able to transfer relatively great traction it is often made of stainless steel, which however is without lubricating characteristics and after continuous loading the above mentioned disadvantages appears.